On 2009-06-23, Aaron Fude wrote:

1. Could it be so heavy that it jeopardizes the stability of the
roof in a roofline application?

Typical closed cell polyurethane foam insulation has a density around
2 lbs per cubic foot. [For exposed roof applications, where the foam
is the finished roof, the density can be higher.] So if you were to
spray it 6 inches deep, which is a lot of foam, that would be 1 lb per
square foot. By contrast, a typical design dead load would be 10 lbs
per square foot, and a design roof live load would be 20 lbs per
square foot, higher in areas with heavy snow.

2. The gas that it traps inside - I'm sure it slowly leaks over time -
what type of gas is it and is it dangerous?

The gas is called a blowing agent, you could try searching on that to
see what information you get. It does slowly leak out over time,
which is part of the reason there is some small degradation in R value
over time.

Cheers, Wayne